I saved a fish! I think…

This is a story that actually happened a few weeks ago but I haven’t been able to stop thinking about it, trying to figure out: am I a hero or a murderer?

It was a beautiful late afternoon, I was riding my bike on the beach with my friend Laurinha.

We’re talking and gossiping when I suddenly scream “LOOK! A FISH!”.

Laurinha almost falls off her bike (it wouldn’t be the first time I make her fall), we stop and walk over to a fish about the size of my hand, flapping desperately, trying to get back to the water.

I look at Laurinha. When I see the scared and doubtful look on her face I realize: I’ve been the one elected to save the fish.

Already feeling the weight of the superhero cape on my back, I carefully pick up the poor little guy and prepare myself to throw it carefully in the water.

As soon as it leaves my hand my brain screams “Shit!” and I’m immediately reminded of my old handball teacher who would scream at me “THIS IS NOT VOLLEYBALL! THROW THAT BALL STRAIGHT!”. The poor fish went 6 ft up in the sky before splashing into the water.

When she was finally able to stop laughing at my demise, Laurinha tried to make me feel better by saying that I “at least gave him a better death”. Great. That’s exactly the hero you’d want around right?

So, here’s the big question. Did that fish die? Was the impact enough to kill it?

I wasn’t going to jump in the water and go all “Finding Nemo” so I settled for the next best thing to ease my consciousness: physics!

It’s funny how a silly question can lead to interesting discoveries, here’s what I think might interest you from all the research I did.

So, before talking about fish, why do people die when they hit the water?

You’ve probably heard someone say that falling into the sea from high distances is the same as crashing into plain concrete. But why is this?

The problem itself is not the water, but actually the falling person! It’s not the water that turns solid, but actually the person that turns “liquid”. Crazy right?

There’s a certain amount of energy that is required to “keep things together” or “pull things apart”, this energy is called “binding energy”. In a free-fall, the body’s kinetic energy is higher than its binding energy (if going at a fast enough speed) and the same behaves like a fluid.

Thus, at high-velocities you have a crash between a “liquid” (the person) and a “liquid” (the water), which would be the same as a crash between a solid and a solid.

But how fast does one need to be going?

There is something in the field of Physics called “Terminal Velocity.” By definition, that would be the maximum velocity that something can achieve during a free-fall. When reaching terminal velocity, chances are that the human being – and any other organism – who fell in the water is dead.

It’s estimated that it takes about 10-14 seconds of free-fall for a person to achieve 99% of its terminal velocity, which would be in the range of 117 to 125 mph. That would be equivalent to a fall of about 1800-1900 feet!

Now, let’s talk fish…

There was a research done in 1972, by Bell and DeLacey. They actually found the terminal velocities of different sized fish by throwing them in the water from a helicopter:

  • Fishes 4-5 inches had a terminal velocity of ~36 mph after a drop of 100 feet.
  • Fishes in the range of 23 inches had terminal velocities of ~130 mph.
  • The survival of fish in the range of 6-7 inches was in the 98% range for drops of 100-300 feet.

The verdict

Considering that the fish (I’m gonna call him Bob because I’m tired of saying fish) I encountered was around 6 inches, it’s terminal velocity was much lower than larger fish (good news for little Bob!). In the Physics language, lower velocity = lower kinetic energy; thus, binding energy of the fish is higher than its kinetic energy and its body behaves like a proper solid. A solid crashing on a liquid = survival. :

And, as indicated in (3), the survival rate for fish in the range of 6-7 inches, which have a slighter bigger terminal velocity, is a whooping 98% for drops of 100-300 feet!

I consider myself a pretty strong girl and I do get confused by the whole feet x meters shenanigan, but I believe it’s safe to say I did not throw Bob 100 feet in the air.

Therefore, I hereby proclaim, by the powers invested in me by the laws of physics and common sense, that I, Luisa, am a fish-hero!

Thank you for reading! 

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